Ring stent

ABSTRACT

A stent arrangement which has at least a first ring ( 3 ) and zig zag struts ( 5 ) extending axially from the periphery of the ring. There can be first and second rings ( 3, 4 ) axially spaced apart and defining substantially parallel planes and a plurality of zig zag portions ( 5 ) between the first and second ring portions around the periphery thereof. The stent can be formed from a single wire or laser cut from a cannula and can be covered or uncovered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of provisional application Ser. No.60/510,242 filed Oct. 10, 2003.

TECHNICAL FIELD

This invention relates to a medical device and in particular to a stentfor endovascular and endoluminal vessel repair and support.

BACKGROUND OF THE INVENTION

Stents are used in surgical procedures to repair or support a bodylumen. Stents may be balloon expandable or may be self expanding. Thatis, stents may be formed from a ductile material and be supplied in acontracted or reduced diameter form to enable deployment to a targetlumen and then expanded to a larger diameter by the use of a balloon. Inanother form a stent may be formed from a resilient material and besupplied in a diametrically or radially constrained form for deliveryand then expanded when radial constraint is removed. Such stents may becovered or uncovered.

Stents proposed by Gianturco (U.S. Pat. No. 5,035,706) have a closed zigzag configuration comprising struts and bends between the struts. Thesestents do not have good dimensional stability because when formed into acylindrical stent, unless constrained, their diameter is not fixed. Thismeans that in some situations, a stent may put more outwardly radialpressure on a vessel than is desirable or it may not be easy to seal astent graft within such a cylindrical stent.

SUMMARY OF THE INVENTION

In one illustrative and preferred embodiment therefore, the invention issaid to reside in a stent arrangement comprising a first ring and asecond ring, the second ring being substantially parallel to and spacedaxially apart from the first ring and a plurality of zig zag portionsextending between and around the peripheries of the first and secondring.

It is the object of this invention to provide a self expanding stentwhich has good dimensional stability.

All of the first ring, second ring and the zig zag portions can be froma portion of wire or a single piece of wire. Preferably the wire is aresilient wire.

Preferably each zig zag portion is formed by struts with a bend betweenadjacent struts. The bend in between the adjacent struts may include ahelix arrangement to put more resiliency into each bend.

Alternatively each zig zag portion is formed by two struts with a bend,a circumferential portion and another bend between adjacent struts. Inthis arrangement the circumferential portion forms part of therespective ring which makes the attachment of the ring to a portion ofgraft material, as discussed below, more secure.

The bends between the struts may be adjacent the rings or incorporateone of the rings into the angle of the bend.

Preferably there are first and second turns of wire in each of the firstring and the second ring.

The terminal end of the wire in each of the first ring and the secondring is preferably provided with a loop so that the stent does notpresent a pointed end of wire which could damage a vessel.

Preferably the at least one ring is a first ring and adjacent alternatebends of the zig zag portion and a second ring is spaced apart from thefirst ring and adjacent an opposite bend of the zig zag portion andthere are at least two turns of wire in the second ring and a terminalend of the wire in the second ring is provided with a loop so that thestent does not present a pointed end of wire which could damage avessel.

In a preferred embodiment, the stent may be produced with first andsecond turns of the wire for the first ring, at least three zig zagpairs of struts extending around the periphery of the ring, a strutextending to the second ring and then at least three pairs of zig zagstruts around the periphery of the second ring and extending backtowards the first ring and then at least two turns of the wire for thesecond ring.

The wires are preferably made of stainless steel, nitinol or otherresilient wire.

The stent, which when completed, is in a substantially cylindrical ordrum form, may be covered or lined with a bio-compatible graft materialor may be used un-lined.

The bio-compatible graft material can include polytetrafluoroethylene,Dacron, Thoralon™, polyamide or any other suitable biocompatible graftmaterial.

While Dacron, expanded polytetrafluoroethylene (ePTFE), Thoralon™, orother synthetic biocompatible materials can be used for the tubulargraft material for the stent graft, a naturally occurring biomaterial,such as collagen, is highly desirable, particularly a specially derivedcollagen material known as collagenous extracellular matrix (ECM)material, such as small intestinal submucosa (SIS). Besides SIS,examples of ECM's include pericardium, stomach submucosa, liver basementmembrane, urinary bladder submucosa, tissue mucosa, and dura mater.

SIS is particularly useful, and can be made in the fashion described inBadylak et al., U.S. Pat. No. 4,902,508; Intestinal Collagen Layerdescribed in U.S. Pat. No. 5,733,337 to Carr and in 17 NatureBiotechnology 1083 (Nov. 1999); Cook et al., WIPO Publication WO98/22158, dated 28 May 1998, which is the published application ofPCT/U.S.97/14855, the teachings of which are incorporated herein byreference. Irrespective of the origin of the material (synthetic versusnaturally occurring), the material can be made thicker by makingmultilaminate constructs, for example SIS constructs as described inU.S. Pat. Nos. 5,968,096; 5,955,110; 5,885,619; and 5,711,969. Inaddition to xenogenic biomaterials, such as SIS, autologous tissue canbe harvested as well, for use in forming the tubular graft material.Additionally Elastin or Elastin-Like Polypetides (ELPs) and the likeoffer potential as a material to fabricate the tubular graft material toform a device with exceptional biocompatibility.

SIS is available from Cook Biotech, West Lafayette, Ind., U.S.A.

To assist with radial compressibility, each of the first and secondrings may be made in a “wavy” form with the apices of the wavesextending towards the other ring.

A stent according to this invention may be used at the ends of legs orarms of stent grafts to give dimensional stability where such arms orlegs engage against the wall of a vessel. The stent can also be used asa short extension affixed to and extending from a fenestration in astent graft to provide a good sealing and dimensionally stable surfacefor an extension arm from the fenestrated stent graft.

The stents according to this invention may be “piggy backed” or stackedwith sequential rings and zig zags to make a longer tubular stent.

In one embodiment the rings and struts of the ring stent can be, forinstance, laser cut from a metallic tube or cannula in a well knownmanner or commercially obtained from a number of stent manufacturers.The metal may be suitably heat treated to make it deformable andresilient.

The stents according to this invention may be manufactured in diametersof from 3 mm to 40 mm and lengths of from 3 mm to 40 mm. Preferably thediameter ranges from about half the length to twice the length and morepreferably the diameter is about the same as the length.

The wire from which the stent in one form may be formed may have adiameter or thickness of from approximately 35 microns to approximately500 microns. Where the stent is formed by laser cutting from a metaltube the diameter of the metal tube may have a diameter of from 3 mm to40 mm and have a wall thickness of from about 35 microns to about 500microns.

In a further form the invention may be said to reside in a stentarrangement comprising at least one of a first resilient ring and asecond resilient ring, the second ring defining a plane which issubstantially parallel to and spaced axially apart from the plane of thefirst ring and a plurality of zig zag portions extending between andaround the periphery of a least one of the first ring and second ring.

Preferably at least one of the first ring and the second ring comprisesa metallic material.

Preferably at least one of the first ring and the second ring is formedfrom a wire or a metal cannula.

The or each ring and the zig zag portions may be formed from a singlepiece of wire.

Each zig zag portion may be formed by struts with a bend betweenadjacent struts.

The bends between the struts may be adjacent the or each ring.

Preferably there are two turns of wire or metal cannula in each of thefirst ring and second ring.

A terminal end of the wire in the or each ring may be provided with aloop so that the stent does not present a pointed end of wire or metalcannula which could damage a vessel.

The at least one ring may be adjacent alternate bends of the zig zagportion and a second ring may be spaced apart from the first ring and ina parallel plane and adjacent the opposite bend of the zig zag portion.

In a further form, the invention is said to reside in a stentarrangement comprising first and second ring portions axially spacedapart and a plurality of zig zag portions between the first and secondring portions around the periphery thereof.

Preferably, each zig zag portion is formed by first and second strutswith a bend in between them.

In a further form, the invention is said to reside in a stent formedfrom a single piece of resilient wire, the stent comprising, in orderalong the wire, at least one first circle or turn of the wire, a firstset of zig zag struts around the periphery of the first turn wire, astrut to a position spaced axially from the first turn, a second set ofzig zag struts around the periphery of the first turn and at least onesecond circle or turn of the wire.

The second circle or turn of wire is preferably substantially co-planarwith the first circle or turn of wire.

In an alternative form the invention is said to reside in a stentarrangement comprising at least one ring formed from a portion of wireand a plurality of zig zag portions extending axially from and aroundthe periphery of the ring.

The or each ring and the zig zag portions are preferably formed from asingle piece of wire and each zig zag portion is formed by struts with abend between adjacent struts. Preferably the bends between the strutsare adjacent the or each ring.

In one embodiment there are two turns of wire in the or each ring. Aterminal end of the wire in the or each ring may be provided with a loopso that the stent does not present a pointed end of wire which coulddamage a vessel.

In a further form the invention is said to reside in a stent arrangementcomprising a first ring formed from a portion of wire, a second ringformed from a portion of wire, the second ring defining a plane which issubstantially parallel to and spaced axially apart from the plane of thefirst ring and a plurality of struts extending between the first ringand the second ring around the periphery of the rings, each of thestruts being angled to the axial direction of the ring.

Preferably the plurality of struts are formed from a continuous piece ofmaterial and the first and second rings are also formed from thecontinuous piece of material.

Preferably there are bends between adjacent struts or there is a bend, acircumferential portion extending around the respective ring and anotherbend between adjacent struts.

U.S. Pat. No. 5,387,235 entitled “Expandable Transluminal GraftProsthesis For Repair Of Aneurysm” discloses apparatus and methods ofretaining grafts onto deployment devices. These features and otherfeatures disclosed in U.S. Pat. No. 5,387,235 could be used with thepresent invention and the disclosure of U.S. Pat. No. 5,387,235 isherewith incorporated in its entirety into this specification.

U.S. Pat. No. 5,720,776 entitled “Barb and Expandable Transluminal GraftProsthesis For Repair of Aneurysm” discloses improved barbs with variousforms of mechanical attachment to a stent. These features and otherfeatures disclosed in U.S. Pat. No. 5,720,776 could be used with thepresent invention and the disclosure of U.S. Pat. No. 5,720,776 isherewith incorporated in its entirety into this specification.

U.S. Pat. No. 6,206,931 entitled “Graft Prosthesis Materials” disclosesgraft prosthesis materials and a method for implanting, transplantingreplacing and repairing a part of a patient and particularly themanufacture and use of a purified, collagen based matrix structureremoved from a submucosa tissue source. These features and otherfeatures disclosed in U.S. Pat. No. 6,206,931 could be used with thepresent invention and the disclosure of U.S. Pat. No. 6,206,931 isherewith incorporated in its entirety into this specification.

PCT Patent Publication No. WO 98/53761 entitled “A Prosthesis And AMethod And Means Of Deploying A Prosthesis” discloses an introducer fora prosthesis which retains the prosthesis so that each end can be movedindependently. These features and other features disclosed in PCT PatentPublication No. WO 98/53761 could be used with the present invention andthe disclosure of PCT Patent Publication No. WO 98/53761 is herewithincorporated in its entirety into this specification.

U.S. Pat. No. 6,524,335 and PCT Patent Publication No. WO 99/29262entitled “Endoluminal Aortic Stents” disclose a fenestrated prosthesisfor placement where there are intersecting arteries. This feature andother features disclosed in U.S. Pat. No. 6,524,335 and PCT PatentPublication No. WO 99/29262 could be used with the present invention andthe disclosure of U.S. Pat. No. 6,524,335 and PCT Patent Publication No.WO 99/29262 is herewith incorporated in its entirety into thisspecification.

U.S. patent application Ser. No. 10/280,486, filed Oct. 25, 2002 andpublished on May 8, 2003 as U.S. Patent Application Publication No.U.S.-2003-0088305-A1 and PCT Patent Publication No. WO 03/034948entitled “Prostheses For Curved Lumens” discloses prostheses witharrangements for bending the prosthesis for placement into curvedlumens. This feature and other features disclosed in U.S. patentapplication Ser. No. 10/280,486, and U.S. Patent Application PublicationNo. U.S.-2003-0088305-A1 and PCT Patent Publication No. WO 03/034948could be used with the present invention and the disclosure of U.S.patent application Ser. No. 10/280,486, and U.S. Patent ApplicationPublication No. U.S.-2003-0088305-A1 and PCT Patent Publication No. WO03/034948 is herewith incorporated in its entirety into thisspecification.

U.S. Provisional Patent Application Ser. No. 60/392,682, filed Jun. 28,2002, and U.S. patent application Ser. No. 10/447,406, filed May 29,2003, and Published on Dec. 18, 2003, as U.S. Patent ApplicationPublication No. U.S.-2003-0233140-A1 entitled “Trigger Wires” discloserelease wire systems for the release of stent grafts retained onintroducer devices. This feature and other features disclosed in U.S.Provisional Patent Application Ser. No. 60/392,682 and U.S. patentapplication Ser. No. 10/447,406, filed May 29, 2003 could be used withthe present invention and the disclosure of U.S. Provisional PatentApplication Ser. No. 60/392,682 and U.S. patent application Ser. No.10/447,406, filed May 29, 2003 are herewith incorporated in theirentirety into this specification.

U.S. Provisional Patent Application Ser. No. 60/392,667, filed Jun. 28,2002, and U.S. patent application Ser. No. 10/609,846, filed Jun. 30,2003, and Published on May 20, 2004, as U.S. Patent ApplicationPublication No. U.S.-2004-0098079-A1, and PCT Patent Publication No. WO2004/028399 entitled “Thoracic Deployment Device” disclose introducerdevices adapted for deployment of stent grafts particularly in thethoracic arch. This feature and other features disclosed in U.S.Provisional Patent Application Ser. No. 60/392,667, U.S. patentapplication Ser. No. 10/609,846, and U.S. Patent Application PublicationNo. U.S.-2004-0098079-A1, and PCT Patent Publication No. WO 2004/028399could be used with the present invention and the disclosure of U.S.Provisional Patent Application Ser. No. 60/392,667, U.S. patentapplication Ser. No. 10/609,846, and U.S. Patent Application PublicationNo. U.S.-2004-0098079-A1, and PCT Patent Publication No. WO 2004/028399is herewith incorporated in its entirety into this specification.

U.S. Provisional Patent Application Ser. No. 60/392,599, filed Jun. 28,2002, and U.S. patent application Ser. No. 10/609,835, filed Jun. 30,2003, and published on Jun. 3, 2004, as U.S. Patent ApplicationPublication No. U.S.-2004-0106978-A1, and PCT Patent Publication No. WO2004/002370 entitled “Thoracic Aortic Aneurysm Stent Graft” disclosestent grafts that are useful in treating aortic aneurysms particularlyin the thoracic arch. This feature and other features disclosed in U.S.Provisional Patent Application Ser. No. 60/392,599, U.S. patentapplication Ser. No. 10/609,835, and U.S. Patent Application PublicationNo. U.S.-2004-0106978-A1, and PCT Patent Publication No. WO 2004/002370could be used with the present invention, and the disclosure of U.S.Provisional Patent Application Ser. No. 60/392,599, U.S. patentapplication Ser. No. 10/609,835, and U.S. Patent Application PublicationNo. U.S.-2004-0106978-A1, and PCT Patent Publication No. WO 2004/002370is herewith incorporated in its entirety into this specification.

U.S. Provisional Patent Application Ser. No. 60/391,737, filed Jun. 26,2002, U.S. patent application Ser. No. 10/602,930, filed Jun. 24, 2003,and published on Mar. 18, 2004, as U.S. Patent Application PublicationNo. U.S.-2004-0054396-A1, and PCT Patent Publication No. WO 2004/002365entitled “Stent-Graft Fastening” disclose arrangements for fasteningstents onto grafts particularly for exposed stents. This feature andother features disclosed in U.S. Provisional Patent Application No.60/391,737, U.S. patent application Ser. No. 10/602,930, and U.S. PatentApplication Publication No. U.S.-2004-0054396-A1, and PCT PatentPublication No. WO 2004/002365 could be used with the present inventionand the disclosure of U.S. Provisional Patent Application Ser. No.60/391,73, U.S. patent application Ser. No. 10/602,930, and U.S. PatentApplication Publication No. U.S.-2004-0054396-A1, and PCT PatentPublication No. WO 2004/002365 is herewith incorporated in its entiretyinto this specification.

U.S. Provisional Patent Application Ser. No. 60/405,367, filed Aug. 23,2002, U.S. patent application Ser. No. 10/647,642, filed Aug. 25, 2003,and published on Apr. 15, 2004, as U.S. Patent Application PublicationNo. U.S.-2004-0073289-A1, and PCT Patent Publication No. WO 2004/017868entitled “Asymmetric Stent Graft Attachment” disclose retentionarrangements for retaining onto and releasing prostheses from introducerdevices. This feature and other features disclosed in U.S. ProvisionalPatent Application Ser. No. 60/405,367, filed Aug. 23, 2002, U.S. patentapplication Ser. No. 10/647,642, filed Aug. 25, 2003, and U.S. PatentApplication Publication No. U.S.-2004-0073289-A1, and PCT PatentPublication No. WO 2004/017868 could be used with the present inventionand the disclosure of U.S. Provisional Patent Application Ser. No.60/405,367, filed Aug. 23, 2002, U.S. patent application Ser. No.10/647,642, filed Aug. 25, 2003, and U.S. Patent Application PublicationNo. U.S.-2004-0073289-A1, and PCT Patent Publication No. WO 2004/017868is herewith incorporated in its entirety into this specification.

U.S. Patent application Ser. No. 10/322,862, filed Dec. 18, 2002 andpublished as Publication No. U.S.2003-0120332, and PCT PatentPublication No. WO03/053287 entitled “Stent Graft With ImprovedAdhesion” disclose arrangements on stent grafts for enhancing theadhesion of such stent grafts into walls of vessels in which they aredeployed. This feature and other features disclosed in U.S. patentapplication Ser. No. 10/322,862, filed Dec. 18, 2002 and published asPublication No. U.S.2003-0120332, and PCT Patent Publication No.WO03/053287 could be used with the present invention and the disclosureof U.S. patent application Ser. No. 10/322,862, filed Dec. 18, 2002 andpublished as Publication No. U.S.2003-0120332, and PCT PatentPublication No. WO03/053287 are herewith incorporated in its entiretyinto this specification.

U.S. Provisional Patent Application Ser. No. 60/405,769, filed Aug. 23,2002, U.S. patent application Ser. No. 10/645,095, filed Aug. 23, 2003,and published on Apr. 29, 2004, as U.S. Patent Application PublicationNo. U.S.-2004-0082990-A1, and PCT Patent Publication No. WO 2004/017867entitled “Composite Prostheses” discloses prostheses or stent graftssuitable for endoluminal deployment. These prostheses and other featuresdisclosed in U.S. Provisional Patent Application Ser. No. 60/405,769,U.S. patent application Ser. No. 10/645,095, and U.S. Patent ApplicationPublication No. U.S.-2004-0082990-A1, and PCT Patent Publication No. WO2004/017867 could be used with the present invention and the disclosureof U.S. Provisional Patent Application Ser. No. 60/405,769, U.S. patentapplication Ser. No. 10/645,095, and U.S. Patent Application PublicationNo. U.S.-2004-0082990-A1, and PCT Patent Publication No. WO 2004/017867is herewith incorporated in its entirety into this specification.

BRIEF DESCRIPTION OF THE DRAWING

This then generally describes the invention but to assist atunderstanding, reference will now be made to the accompanying drawingswhich show some preferred embodiments of the invention.

In the drawings:

FIG. 1 shows a perspective view of a first embodiment of stent accordingto this invention;

FIG. 2 shows the stent of the embodiment of FIG. 1 with an internalcovering of a biocompatible graft material;

FIG. 3 shows the stent of the embodiment of FIG. 1 with an externalcovering of a biocompatible graft material;

FIG. 4 shows an alternative embodiment of a stent according to thisembodiment;

FIG. 5 shows a still further embodiment of a stent according to thisinvention;

FIG. 6 shows a plan view of a stent according to this invention;

FIG. 7 shows a side elevation of a stent according to this invention;

FIG. 8 shows an embodiment of a stacked stent according to thisinvention;

FIG. 9 shows an embodiment of this invention used as a stent on the endof a leg of a bifurcated stent graft;

FIG. 10 shows a perspective view of a alternative embodiment of theinvention;

FIG. 11 shows a developed view of a further alternative embodiment ofthe invention;

FIG. 12 shows a perspective view of the alternative embodiment of theinvention shown in FIG. 11;

FIG. 13 shows a perspective view of the alternative embodiment of theinvention; and

FIG. 14 shows a perspective view of the further embodiment of theinvention.

DETAILED DESCRIPTION

Now looking more closely at the drawings and in particular FIG. 1, itwill be seen that the stent 1 according to one embodiment of thisinvention comprises a first resilient ring assembly 3 and a secondresilient ring assembly 4 spaced (preferably parallel) to and axiallyaway from the first ring assembly 3 and a number of zig zag struts 5between the first resilient ring assembly 3 and the second resilientring assembly 4. The first and second resilient ring assemblies and thestruts comprise a metallic wire.

Although metal or metal alloy materials are preferred other resilientmaterials such as polymers, carbon fibres and other biocompatiblematerials are also contemplated.

The first ring assembly 3 commences at a loop 7 of the wire and isformed from two circles or turns of wire 9 and then at 11 there is abend and the wire is angled in a first strut 13 extending to a bend 15adjacent the second ring assembly 4 and then a further angled strut 17to a bend 19 adjacent the first ring assembly 3. Consecutive angledstruts and bends extend around the periphery of the ring assembly 3 andthe ring assembly 4 from the bend 19 until bend 21 adjacent to the bend11 where there is an axial strut 23 extending to the second ringassembly 4 and a bend 25. From the bend 25 is an angled strut 27 whichextends to the first ring assembly 3 where there is a bend 29 and asubsequent angled strut 31. Subsequent angled struts and bends extendaround the periphery of the second ring assembly 4 and first the ringassembly 3 from strut 31 to a bend 33 adjacent to bend 25 where the wireextends to a first circle or turn 35 of the ring assembly 4 and then toa second turn 37 of the ring assembly 4 to finally terminate in a loop39 of the wire.

The wire in this embodiment is preferably nitinol and has a diameter of150 microns and the stent has a diameter of 8 mm and a length of 9 mm.There are three sets of struts with a bend between them extending fromeach of the rings to the other of the rings giving a total of twelveangled struts and one axial strut.

By this arrangement a stent with good radial dimensional stability isformed because the rings restrict radial expansion and contraction butbeing formed from resilient wire has good compressibility to enable itto be deployed endoluminally in a contracted state.

FIG. 2 shows an embodiment of the stent shown in FIG. 1 with abiocompatible graft material lining. The graft material 40 is retainedby stitching 41 to the first ring assembly 3 and by stitching 42 to thesecond ring assembly 4. Stitching 44 is also provided to retain thegraft material into a cylindrical shape where the struts cross betweenthe first and second rings. By this arrangement a portion of stent graftis formed which has good dimensional stability and which may be mountedto or provided on the end of a stent graft, on the leg of a stent graft,or as or on a side arm from a stent graft.

The graft material may be Dacron, Thoralon™ material, nylon or any othersuitable material such as collagenous extracellular matrix (ECM)material including small intestine submucosa, which is commerciallyavailable from Cook Biotech, West Lafayette, Ind., U.S.A.

Similarly in FIG. 3 a biocompatible graft material covering 50 isprovided on the outside of the stent 1 with the material 50 sewn to andretained onto the first ring assembly 3 by stitching 51, onto the secondring assembly 4 by stitching 52 and to the struts by stitching 53.

FIG. 4 shows a further embodiment of a stent according to thisinvention. In this embodiment the first ring 60 and the second ring 61of the stent are formed as a wavy ring with the waves extending axiallyso that there are alternate troughs 62 and crests 63. The crests 63correspond substantially with the bends 64 between struts 65 of the zigzag portion 66 of the stent. The apices 62 extend towards the ring 61.The wavy rings can be formed so that their rest diameter issubstantially the desired final diameter of the stent.

These wavy rings, while still providing good dimensional stability,allow radial compression of the rings 60 and 61 as well as the zig zagportion 66. This will assist with enabling this form of the stent to beradially compressed onto a delivery device as required.

FIG. 5 shows a still further embodiment of a stent according to thisinvention. In this embodiment, the stent has a two-circle or turn ring70 of wire at its upper end, a two-circle or turn ring 72 of wire at itslower end and a number of zig zag struts 74 of wire between the rings 70and 72. In this embodiment, however, all of the pairs of struts commenceat the ring 70 and after six pairs of zig zag struts, a single strut 76extends to the ring 72 to complete the stent with the two turns of thesecond ring. Rather than the axial strut 76 there may be a furtherangled strut between the first ring 70 and the second ring 72. In thisembodiment the bends 73 incorporate the ring 70 within the acute angleof the bend and the bends 75 incorporate the ring 72 within the acuteangle of the bend.

FIG. 6 shows a plan view of the stent shown in FIG. 1 and it will benoted that the stent in plan view is substantially cylindrical and thering 3 and the termination loops 7 and 39 can be seen.

FIG. 7 shows a side elevation view of the stent similar to that shown inFIG. 1 except that at the apex of each of the bends there is a helixarrangement 38 to give more resilience to each bend. It will be notedthat the zig zag struts 5 provide an essentially cylindrical peripheralsurface to the stent.

FIG. 8 shows a further embodiment of a stent in which there is a firstring 80, a second ring 82, a third ring 84 and a fourth ring 86. Betweeneach pair of rings there is a zig zag strut portion 88. The stentaccording to this embodiment of the invention can be made from a singlelength of wire commencing with the loop 89 on the ring 80 andterminating with the loop 90 on the ring 86.

By this arrangement, a substantially cylindrical elongated stent can beformed without welds which could introduce weakness into the stent.

FIG. 9 shows an arrangement of bifurcated or branched stent graftaccording to this invention using a stent of the present invention.

The stent graft comprises a tubular main body 100 with well-knownGianturco type zigzag Z stents 102 along its length. Extending from abifurcation 103 in the tubular body 100 is a side arm 104. The side arm104 has a Gianturco type zig zag Z stent 105 and terminates in a ringstent 106 of the type disclosed in this invention. The use of the stentgraft 106 on the side arm 104 provides a diametrically stable arm intowhich an extension leg or arm can be inserted with good reliability forsealing into the side arm either using a covered self expanding stent ora covered balloon expandable stent.

FIG. 10 shows a perspective view of a still further embodiment of astent according to this invention. In this embodiment, the stent has twocircles or turns of wire 109 starting with a loop 111 to form a ringassembly 110 of wire at its upper end and a number of zig zag struts 112of wire extending axially from the circumference of the rings 110. Inthis embodiment, however, all of the pairs of struts 112 commence at thering 110 and after six pairs of zig zag struts 112 a partial turn ofwire 114 follows the ring 110 and terminates in a loop 116 to completethe stent. The stent of this embodiment may be particularly useful formounting onto a leg or arm of a stent graft to provide dimensionalstability at its end.

FIG. 11 and FIG. 12 show a further alternative embodiment of theinvention.

FIG. 11 shows a stylised or developed view of a stent according to anembodiment of the invention laid out flat to show the continuous strandof Nitinol or stainless steel formed into the rings and struts. FIG. 12shows the stent of FIG. 11 in a perspective view. In this embodimentthere are in effect five sets of bends at each ring of the stent butthere may be other odd numbers of sets of bends such as seven or nine.

The stent 120 of this embodiment has a single continuous length ofmaterial such as wire starting at loop 122 and forming a first ring 124to a bend 126 and then a first angled strut 128 to another bend 130 andthen into a second ring 132 which is spaced apart, essentially coaxialwith and parallel to the first ring 124. The second ring 132 has one andone fifth turns and then a bend 134 and then an angled strut 136 to thefirst ring and a bend 138. Beyond the bend 138 there is acircumferential peripheral portion 140 essentially parallel and adjacentto the first ring 124 to a further bend 142. There are then alternatestruts and peripheral portions with bends in between them of thecontinuous length of material making a total often struts in all endingwith bend 144. After the bend 144 the continuous length of materialextends in a circumferential peripheral portion 146 essentially paralleland adjacent to the first ring 124 to a terminal loop 148. It will benoted that by this arrangement there is at all portions of each ring atleast two portions of the wire or other continuous material.

By the arrangement of this embodiment of the invention the sharp bendsof the earlier embodiments between the zig zag struts do not exist andthe short peripheral portions between bends become part of the ring andcan be sutured to graft material making a more secure structure.

FIG. 13 shows a perspective view of the alternative embodiment of theinvention. In this embodiment the stent 150 is formed from a tube orcannula of metal or other material and can be, for instance, laser cutfrom the tube or cannula in a known manner. The material of the stent150 is resilient so that the stent is deformable.

The stent 150 includes a first resilient ring 152 and a second resilientring 153 spaced apart axially from the first ring 152, and a pluralityof diagonal or zig zag struts 154 around the periphery and between thefirst and second resilient rings. In this embodiment the struts 154 meetin between the first and second rings at 155 but in an alternativeembodiment the struts may not cross between the first and second rings.FIG. 13 shows a squat ring stent according to the invention, that is,the height is about half the diameter.

FIG. 14 shows a perspective view of the alternative embodiment of theinvention. In this embodiment the ring stent is formed from a tube orcannula of metal or other material and can be, for instance, laser cutfrom the tube or cannula in a known manner. The material of the stent160 is resilient so that the stent is deformable.

The ring stent includes a first resilient ring 162 and a secondresilient ring 163 spaced apart axially from the first ring 162, and aplurality of diagonal or zig zag struts 164 around the periphery andbetween the first and second resilient rings. The struts cross betweenthe first ring 162 and second ring 163 to form junctions 165. In thisembodiment the ring stent is tall rather than squat, that is, the heightis about twice the diameter.

Throughout this specification various indications have been given as tothe scope of the invention but the invention is not limited to any oneof these but may reside in two or more combined together. The examplesare given for illustration only and not for limitation.

1. A stent arrangement comprising a first resilient ring and a secondresilient ring, the second ring being substantially parallel to andspaced axially apart from the first ring and a plurality of zig zagportions extending between and around the periphery of a least one ofthe first ring and second ring.
 2. A stent arrangement as in claim 1wherein at least one of the first ring and the second ring comprises ametallic material.
 3. A stent arrangement as in claim 1 wherein at leastone of the first ring and the second ring comprises at least one of awire and a metal cannula.
 4. A stent arrangement as claim 1 wherein atleast one of the first ring and the second ring and the zig zag portionscomprise a single piece of wire.
 5. A stent arrangement as in claim 1wherein each zig zag portion including a plurality of struts with a bendbetween adjacent struts.
 6. A stent arrangement as in claim 5 whereinthe bends between the struts are adjacent at least one of the first ringand the second ring.
 7. A stent arrangement as in claim 3 wherein thefirst ring and second ring each includes first and second turns of theat least one of the wire and the metal cannula.
 8. A stent arrangementas in claim 3 wherein a terminal end of the wire in each ring isprovided with a loop, whereby the stent does not present a pointed endof wire or metal cannula which could damage a vessel.
 9. A stentarrangement as in claim 1 wherein the first ring is adjacent alternatebends of the zig zag portion and the second ring is spaced apart fromthe first ring and adjacent an opposite bend of the zig zag portion. 10.A stent arrangement comprising at least one ring of a portion of wireand a plurality of zig zag portions of a portion of wire extendingaxially from and around a periphery of the ring.
 11. A stent arrangementas in claim 10 wherein the ring and the zig zag portions comprise asingle piece of wire.
 12. A stent arrangement as in claim 10 whereineach zig zag portion includes struts with a bend between adjacentstruts.
 13. A stent arrangement as in claim 10 wherein each zig zagportion includes at least two struts with a bend between, acircumferential portion and another bend between adjacent struts.
 14. Astent arrangement as in claim 12 wherein the bends between the strutsare adjacent the ring.
 15. A stent arrangement as in claim 10 whereinthere are at least two turns of wire in the ring.
 16. A stentarrangement as in claim 10 wherein a terminal end of the wire in thering includes a loop, whereby the stent does not present a pointed endof wire which could damage a vessel into which it is deployed.
 17. Astent arrangement as in claim 10 wherein the ring is adjacent alternatebends of the zig zag portion and a second ring is spaced apart from thefirst ring and adjacent an opposite bend of the zig zag portion.
 18. Astent arrangement as in claim 17 wherein there are at least two turns ofwire in the second ring and a terminal end of the wire in the secondring includes a loop so that the stent does not present a pointed end ofwire which could damage a vessel.
 19. A stent arrangement comprising afirst ring formed from a portion of wire, a second ring formed from aportion of wire, the second ring defining a plane which is substantiallyparallel to and spaced axially apart from the plane of the first ringand a plurality of zig zag portions extending between and around theperiphery of the first and second rings.
 20. A stent arrangement asclaim 19 wherein the stent is in a substantially cylindrical or drumform and is covered or lined with a bio-compatible graft material.
 21. Astent arrangement as claim 19 wherein each of the first and second ringsis made in a “wavy” form with the apices of the waves extending towardsthe other ring.
 22. A stent arrangement as claim 19 wherein the stent isstacked with sequential rings and zig-zags to make a longer tubularstent.